Short answers, pulled from the story.
The Treaty of Shimoda designated Iturup as Japanese territory while assigning Urup and all northern islands to Russia. The treaty also recognized Kunashiri, Shikotan, and the Habomai Islands as belonging to Japan.
Soviet forces invaded the Kuril Islands starting on the 18th of August 1945 following a declaration of war on the 8th of August 1945. Japanese inhabitants living on these islands were expelled from their homes two years later during the complete removal of the existing population.
Japan renounced all rights to the Kuril Islands in the treaty but the document did not explicitly recognize Soviet sovereignty over them. The Soviet Union refused to sign this document because it lacked explicit language confirming their ownership of the territories.
The Joint Declaration offered to return only two small islands named Shikotan and Habomai in exchange for a peace treaty. Japan declined the offer initially because they demanded all four disputed islands be returned rather than just the smaller ones.
Dmitry Medvedev ordered advanced weapons including Bal rocket systems stationed in Kunashir and Bastion systems placed on Iturup by the 25th of March 2016. S-300V4 versions of the missile system were deployed for combat duty on Iturup in December 2020 while coastal defense systems arrived at Paramushir on the 22nd of March 2023.
Kenjiro Suzuki heads the Tokachi branch of the organization which had a budget of approximately 187 million yen in 2008 to support displaced families. Public polling in July 2009 showed 89% of Russians opposed territorial concessions to Japan compared to only 7% support in May 2016.